Such heating elements are usually called hollow cartridges in this branch of industry. They are equipped with a coiled tube cartridge, which is pressed into circumferential grooves of a brass tube or CrNi steel tube. The circumferential grooves and the coiled tube cartridges pressed into same usually extend in a thread-like manner with different pitches to make it possible to set an adequate temperature distribution along the component to be heated. Such a component may be, e.g., a plastic injection nozzle. To obtain good heat transmission to the nozzle body of, e.g., such a plastic injection nozzle, the tube is provided with an accurately fitting internal diameter, i.e., with a fitting hole. The nozzle body itself, which is also called “material tube,” may be provided with a one-layer, two-layer or multilayer tube wall.
A hot channel nozzle for an injection molding means designed as an injection mold, in which a tubular hollow body consisting of metal, which is pushed over the material tube of the nozzle body, is provided with a tubular heating body pressed into circumferential grooves, is known from DE 20 2006 018 576 U1. This hollow body, which is called a sleeve there, is also equipped with a temperature sensor, which is accommodated in a separate circumferential groove and which is needed as a temperature regulating means. The tube wall of the hollow body or of the sleeve is provided at one end with a radial passage opening. According to one embodiment, the free end, i.e., the tip of the temperature sensor, protrudes freely into this passage opening and is brought into contact with the material tube by means of a wave-shaped clamp. The two ends of the clamp are supported now on the inner edges of the passage opening, while their middle part surrounds the temperature sensor on the outside.
It shall thus be achieved that the free end of the temperature sensor, which acts as a measuring point, will not measure the temperature of the heated sleeve or of the heated hollow body, but will detect the temperature of the material tube of the nozzle.
Provisions are made in another embodiment for the end section of the temperature sensor to pass through a front-side recess of the sleeve or of the hollow body. The fixation or local fastening shall now be brought about by bonding, soldering or the like, or even by means of a clamp.
In all these types of embodiment, the rounded tip or the free hemispherical end of the temperature sensor is in contact with the material tube of the nozzle by a punctiform or at best linear contact, which is disadvantageous in terms of measurement technique because of the low heat transmission.